VANCOUVER, Wash. – When possession of small amounts of marijuana becomes legal in Washington in three days, there will be a DUI limit of five nanograms of THC that you can have in your blood.

But how will police officers detect that in drivers?

There will be specially trained officers to figure out how much THC is in a driver's blood. They're called Drug Recognition Experts or DREs for short.

They've actually been around for a long time. But now that some of the stigma of having pot is being lifted, more people may be willing to smoke it and get behind the wheel stoned.

There are about a dozen police officers in Clark County trained as DREs to recognize the signs of when people are high on pot, cocaine, heroin and prescription medications.

Officers like Ryan Martin with the Vancouver Police Department can tell if someone is high on pot or other drugs based on a series of eye tests. For example, if drivers can't cross their eyes, they’re likely high. There are other tests, too, that require the driver to hold his balance while counting at the same time.

"We're looking to see if there's any sway while your foot's up; we're looking to see if your arms come out for balance; we're looking to see if you put your foot down, and we’re also looking to see if you start hopping because you start to lose your balance," said Martin. "So there're four clues, and what the studies done by the National Highway Traffic Safety Administration (show), two clues of impairment are enough to suggest that somebody is impaired."

He said someone’s perception of time is also affected while under the influence of marijuana. That's because time tends to slow down for people high on pot so their counting slows down. People on meth speed their counting up.

Officers will also test to see if drivers can follow directions to find out "their ability to focus on what you told them to do," Martin said.

There aren't any devices that exist like a Breathalyzer to test people along the roadside for pot and other drugs. But if a driver fails a DRE's roadside test, the driver will be brought to the police station for a lot more testing, including a blood draw. But the blood test results take six to eight weeks to come back.

Plus: "If the person is not cooperative and not willing to provide a blood sample, then we can get a blood search warrant," Martin said.
But getting the search warrant takes time.

Even if the blood sample shows a lower level than the five nanograms of THC, someone can still be charged with DUI if the officer believes the tests show the driver is impaired. That’s also how it works with alcohol and the .08 limit.

Checking a drunken driver is much, much easier. It takes two to three times longer to test and process a driver who's high on drugs.

Washington voters passed Initiative 502 last month. It will allow anyone 21 or older to have up to an ounce of pot.